Biomedical science has twin goals; to explain the many amazing properties of our own bodies and those of other animals, and to use this information to reveal the causes of disease and to suggest possible treatments. We work at the interface between cell and developmental biology, focusing on the epithelial tissues that form the basic architectural unit of our bodies and of those of other animals. We explore how the machinery mediating cell adhesion, cytoskeletal regulation and Wnt signaling regulates cell fate and tissue architecture in development and disease. Epithelial tissues like skin, lung, colon, and breast are affected in many cancers. Cancer results from alterations in normal cell behaviors. To explore underlying causes of epithelial tumors, we need to understand the basic cellular machinery that links cell adhesion, signal transduction and cytoskeletal regulation during normal development.

We focus on the machinery that modulates cell-cell adhesion and connects cell junctions to the actin cytoskeleton, thus shaping the architecture of epithelial tissues. We also explore the machinery that transduces and regulates Wnt signaling, which helps determine cell fates. Wnt signaling is inappropriately activated in colon and other cancers, while the cell adhesion machinery is inactivated in most metastatic tumors. We study these processes in the fruit fly Drosophila, combining classical and modern genetic tools with state-of-the-art cell biology, microscopy, and biochemistry, thus capitalizing on the speed of this model system and its synergy with vertebrate cell biology, and supplement this with work on cultured Drosophila cells and mammalian cells. Like all good science, our work sometimes leads us in unexpected directions–our recent work on the roles of centrosomes in genome stability is an example.

Wnt signals are one of the five signal transduction pathways that shape virtually all cell fates and which are inappropriately activated in most solid tumors. The key regulated effector of Wnt signaling is the protein ß-catenin. Wnt signaling acts by regulating its stability. In the absence of Wnt signaling, ß-catenin is targeted for proteasomal destruction by a multi-protein complex called the destruction complex. In the presence of Wnt signals, the destruction complex is inactivated, and ß-catenin levels rise, allowing it to enter the nucleus and work with TCF proteins to regulate Wnt target genes. In our lab, we seek to determine how the tumor suppressor APC, a key component of the destruction complex, regulates both Wnt signaling and the cytoskeleton. We use both the fruit fly Drosophila and cultured human colon culture cells to unravel the mechanisms by which APC works. We combine powerful genetic tools and state of the art microscopy. We are currently exploring how APC regulates assembly and disassembly of the destruction complex as part of a catalytic cycle. We are also exploring separate roles APC plays in regulating the cytoskeleton and thus ensures high fidelity chromosome segregation, and branching off from this the interplay between mitotic fidelity regulators, checkpoints and apoptosis which maintains genome stability. Finally, we explore novel biological roles for Wnt signaling during development.

Figure 3. Armadillo-GFP localization to cell-cell junctions during dorsal closure in a living embryo.

In studying adhesion, our challenge is to alter our static model of adhesion to explain the remarkable cellular events of morphogenesis that shape the embryonic body plan and build tissues and organs. To do so, we must understand the dynamic regulation of cell adhesion and how it is coordinated with the cytoskeleton. We visualize these processes via state-of-the art confocal microscopy and live-imaging, using fluorescently-tagged versions of adhesion and cytoskeletal regulatory proteins, as well as probes that allow us to visualize the actin and microtubule cytoskeletons. This allows us to examine cell behavior and the cell biological events underlying it during dynamic events of morphogenesis, such as dorsal closure. In searching for regulators of adhesion and the cytoskeleton, we have focused on the non-receptor tyrosine kinase Abelson (Abl). Mutations in Abl cause two forms of human leukemia. We found that Abl coordinately regulates adhesion and the dynamics of the actin cytoskeleton. We are currently exploring the mechanisms by which Abl regulates complex events of morphogenesis. We also are exploring the functions of proteins that directly regulate actin dynamics, including Diaphanous-class formins and Enabled/VASP proteins, some of which are targets of Abl. In parallel, we are examining proteins that help form the dynamic links between the cadherin-catenin complex and the actomyosin cytoskeleton. We focus on the small GTPases Rap1 and the junctional protein Canoe/Afadin. In addition to their role in adhesion, these proteins also regulate cell polarity, and we are actively pursuing their roles in both apical-basal and planar polarity.

To learn more about our work, visit our lab website via the link above, where you can meet the people in the lab and learn more about their work. It’s an exciting time to be working at the interface between cell and developmental biology, and we are always looking for talented and enthusiastic graduate students and postdocs to add to our group. You can also follow us on Facebook or check out our videos on Vimeo.

Obtaining Armadillo Antibody

The anti-Armadillo antibody is now available from the Developmental Studies Hybridoma Bank, an NIH funded facility that produces antibodies for the research community at cost. They will sell you anti-Armadillo 7A1 mouse monoclonal antibody at $10/ml. You can reach them by phone at 319-335-3826 or by email at dshb@uiowa.edu. Perhaps the easiest way to reach them is at their home page at http://dshb.biology.uiowa.edu/.

If you need more information about the use of the antibody, feel free to contact us. We use it at 1:40 in situ on embryos, 1:20 for immunoprecipitations, and at 1:400 on Westerns.

Good luck with your experiments.

Figure 4. Armadillo protein is normally found in the adherens junctions surrounding each cell. However, in cells which have received Wingless signal, Armadillo protein also accumulates in the cytoplasm and the nucleus, where we suspect it may be involved in activating transcription of target genes. Panel A shows an embryo double labeled with anti-Armadillo antibody (red) and anti-Engrailed antibody (green). Engrailed is a transcription factor and marks the nucleus. Some nuclei are yellow, showing co-localization of Armadillo and Engrailed in the nuclei of cells receiving Wingless signal. Panels B and C are the single labeled images.

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